1. Field of the Invention
The present invention relates to a bias circuit and a power amplifier with a dual-power mode applicable to a wireless communications system.
2. Description of the Related Art
In general, a wireless communications scheme is a digital modulation/demodulation scheme having an appropriate scheme in terms of frequency usage efficiency enhancement employed therein. For example, a cell phone based on a code division multiple access (CDMA) scheme employs a quadrature phase shift keying (QPSK) scheme, and a wireless local area network (WLAN) following the IEEE (Institute of Electrical and Electronics Engineers) 802.11 communications standard employs an orthogonal frequency division multiplexing (OFDM) digital modulation scheme.
A wireless communications system employing a wireless communications scheme includes a power amplifier amplifying power of a transmission signal.
Here, a system requiring linear amplification requires a power amplifier having linearity in order to amplify a transmission signal without distortion. Here, linearity refers to characteristics in which, even in the case that power of an input signal is changed, power of an output signal is amplified at a predetermined ratio and a phase thereof is not changed.
Also, in order to increase usage time of a device with limited battery capacity, a technique of increasing efficiency by significantly reducing power consumption of components therein is required for a wireless communications device.
An existing power amplifier provides a bias voltage generated by a bias circuit to a power amplification device through a resistor. Here, the bias circuit may have a temperature compensation function.
However, since existing, already designed, power amplifiers, in the design thereof provide a fixed bias voltage, not allowing for a high power mode or a low power mode to be selected as necessary, it maybe difficult to appropriately cope with transmission power required for the characteristics of an applied wireless communications system or a communications environment.
The Related Art Document below relates to a power amplifier, which, however, does not disclose technical matters for selecting a high power mode or a low power mode to reduce power consumption.